In an oil or gas drilling operation, the derrick is the support structure for the equipment used to lower and raise the drill string into and out of the wellbore. The drill string is a column of coupled drill pipes and drill collars that transmit torque and drilling fluid to the drill bit. Either a kelly drive or a top drive apparatus provides the torque to rotate the drill string and induce cutting and crushing of subterranean earth digging by the drill bit. Drill collars comprise the section of the drill string nearer the drill bit and are heavy, thick-walled tubes used between traditional drill pipe and the bit in the drill stem. The increased mass of the thicker collars provides increased downward force for the drill bit. As drilling depth increases, drill pipes are inserted between the derrick and the heavier drill collars.
The drill depth may reach many thousands of feet. Although the drill bit is made of hard materials, such as tungsten carbide, and continuously lubricated with drilling fluid, drill bit wear is inevitable. Consequently, the entire drill string must be removed several times during the drilling process to replace worn drill bits. The drill string may also be removed for replacing other equipment, running casing, or other reasons. The drill string removal and replacement process is known as “tripping pipe.”
During the pipe tripping process, a portion of the drill string is pulled out of the well bore and up into the derrick. Drill pipes, typically about 30 ft in length, are removed in sections of coupled drill pipes called pipe stands. The number of drill pipes that comprise a pipe stand is governed by the height of the derrick. Pipe stands typically comprise 3 coupled drill pipes, but may comprise 2 or 4 coupled drill pipes. As the drill string is pulled out from the well bore, a pipe stand is threadably uncoupled from the drill string below. An uncoupled pipe stand is suspended by elevators attached to a drill line more than 90 ft. above the drill floor.
A typical five man drilling crew comprises two floorhands and a derrickman, who employ heavy equipment and physical strength to disassemble and reassemble a pipe string and temporarily store pipe stands during the tripping process. The lower portion of a pipe stand rests on one end of the drill floor called the setback area. The upper portion of a pipe stand is racked within the fingers of a racking board. In a concerted effort, the derrickman pulls the top of a suspended drill stand away from the well bore center line while a floorhand pushes the lower portion of the suspended pipe stand to the setback area. The drill line lowers the pipe stand onto the setback area of the pipe rack floor. The derrickman racks the upper portion of the drill stand within the racking board for temporary storage during the tripping process. The process is repeated until all the pipe stands and collars, often comprising a total of thousands of feet in length, have been removed. After replacement of the drill bit or other equipment, this process is reversed to reinsert all the pulled collars and pipe stands into the well bore to continue the drilling process.
The pipe tripping process is extremely dangerous. Rig personnel are working alongside heavy equipment and machinery capable of exerting exceedingly powerful forces. The derrickman works unaccompanied more than 90 ft above the drill floor. The drilling process usually continues for 24 hours a day, despite adverse weather conditions. Drilling mud, a viscous but slippery hydrated polysaccharide suspension, spills out of drill pipes, litters the drill floor and equipment, and obscures safety goggles. Human error, fatigue, extreme weather conditions, and chemical contaminants contribute to the dangers of pipe tripping. The International Association of Drilling Contractors (IADC) recognizes pipe tripping as the operation that involves the most lost-time and recordable injuries. The IADC recognizes drill pipes and collars as the equipment responsible for the most lost time after drilling rig accidents.
The drilling industry has attempted to address the dangers associated with personnel working on the drilling floor by developing mechanical pipe handling equipment.
U.S. Pat. No. 3,633,767 describes a pipe-racking apparatus employing a pantographic transfer arm that telescopes toward the well bore center line to retrieve pipe stands. U.S. Pat. No. 4,013,178 describes a pipe racker with a maneuverable arm that can pivot about an axis but requires an additional cable-lift system for handling drill collars. U.S. Pat. No. 4,044,895 describes a pipe racking apparatus comprising a pivotally mounted chute that positions single drill pipes, but not pipe stands, within a container. U.S. Pat. Nos. 4,117,941 and 4,274,778, and 4,621,974 describe devices for handling and racking drill pipes comprising upper and lower manipulators, requiring significant modification of upper and lower sections of the derrick. U.S. Pat. No. 4,345,864 descries a pipe stand moving apparatus having a gripping head mounted to a cantilever arm, but relies on several moving parts for operation including a worm gear, chains, drive sprockets, and other gears. U.S. Pat. No. 5,183,122 describes a derrick for raising or lowering drill string comprising a derrick frame, a rack, a gantry, and a pipe gripping unit. U.S. Pat. No. 6,343,662 describes a hydraulic drilling rig with a movable pipe support cradle that transfers pipe stands to a storage area. U.S. Pat. No. 6,821,071 describes an automated pipe racking apparatus with a rotatable arm support member that moves the top of a pipe stand and base grids mounted on the drill floor. U.S. Pat. No. 7,731,746 describes a pipe manipulator arm mounted to a rotatable assembly attached to the derrick.
The mechanical pipe handling equipment of the prior art includes integrated mechanisms for movement in forward, rear, up, and down directions and circular or rotational movement. The mechanical integration of the mechanisms responsible for movement in multiple directions requires complicated equipment that is difficult to service. There is a need in the art for a simple, compact, efficient, stable mechanical pipe handling apparatus that obviates the need for a derrickman and can be attached to an existing derrick. There is also a need in the art for a mechanical pipe handling apparatus that separates the mechanisms responsible for forward and rear, up and down, and rotational movement. While the invention has been described with a certain degree of particularity, it is to be noted that many modifications may be made in the details of the invention's construction and the arrangement of its components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification.